Tape, cardboard, scissors. Use multiple pieces of cardboard and cut out shapes to fit the corners. Then piece it all together and tape it into one piece. One step up from that would be to get something like this.

General Tools 833 Plastic Contour Gauge, Profile Gauge, Shape Duplicator, 10-Inch (254mm), Precisely Copy Irregular Shapes For Perfect Fit and Easy Cutting - Profile Gauge - Amazon.com

General Tools 833 Plastic Contour Gauge, Profile Gauge, Shape Duplicator, 10-Inch (254mm), Precisely Copy Irregular Shapes For Perfect Fit and Easy Cutting - Profile Gauge - Amazon.com

www.amazon.com

 

Or a trash bag and some two part foam, and make a mould against the side.
Then fibreglass over that side and you should be pretty close.

You will not want let any of the foam escape as it will stick to carpet really well.

If the said of the box is think, then you need to account for that... maybe a layer of neoprene on the side between the foam bag and the surface?

 

In a pinch you can use a metal clothes hanger. Just unwind the hook and straighten the hanger out and Then bend to make your form.

 

Also a role of the metal you get from Lowe’s that is about 3/4 inch wide and has holes in it. Not sure what’s it’s called but I use it to make mounting brackets for tweetes in the dash when necessary. It’s bendable but holds its shape.

I just remembered. It’s a role of metal strapping to hold up hvac ducts or plumbing underneath the house. Very handy stuff

 

I remember seeing a few techniques for this on some CAF videos. I feel like you could replicate this same process without all the fancy tools, I know I've heard some using a pencil and a washer, but you could just as easily use something else. Could even bust out your hole saw and make your own and in a custom radius!

"Compass" Method:

"Washer" Method:

 

I fit my baffle to the car for IB, the bar in there and the rear deck. I used cardboard it works great, even if you mess it up you just grab a new piece. I always used cardboard for deck patterns and baffles even shaped boxes. You can get it for free (boxes) or look harder and find tv boxes or from large things like house doors, etc. I use a marker and box cutter, tape, stapler for small areas. You could make a nice IB setup there it does not have to seal perfect. Use foam and carpet to seal it and make it open up like a shelf, I have done that in hatchbacks with great success. It may depend on how often you think you will use that rear area. Then you can pack bags and stuff under it if you really need to, or make the whole thing removable. One car I had a trailer plug on the sub box, just unplug and take it out if I needed the room for a special trip.

 

Buy a flexible ruler. It keeps it shape quite well. Then trace it to cardboard for a test fit, then to MDF.

Super useful.

 

Where have you been all my life!

 

I found mine at a craft/sewing store years ago. As soon as I saw it, I thought the same thing.

 

Flexible rulers are awesome. I believe I showed you them with my boy's Civic build.

 

Wow, pretty sweet.

 

And only $10!

 

I made a dozen trunk floors like this when I worked at a shop. goes like this:

1. measure the distance between the wheel wells. Cut the main floor this wide, front to back. The sides are straight. The side that butts up against the rear seats is straight. Usually there is a minor curve to the back that isn't too hard, but if you can't trace it, just follow what is done for the sides for this part and it'll work.

So, figuring you have the main floor done, you make the "wings":

2. Cut a bunch of cardboard into strips about 15" x 2". We always had cardboard laying around.
3. grab a piece of scrap MDF. we always had scrap MDF laying around.
4. Put MDF in trunk at the level of the floor.
5. take a strip of cardboard and put the 2" section against the contour of the trunk. staple it to the scrap
6. take another strip and put it against the trunk contour. staple.
7. Repeat until you have a whole series of strips up against the contour you want to cut, 2" at a stretch.
8. Pull the scrap and trace it onto a piece of MDF that will become the "wing". Or, if you will make a template, trace it onto some 1/4" hardboard to make the template.
9. Jigsaw the wings
10. test fit

11. Upholster. lay the fabric down, apply the spray glue, and drop the false floor pieces, all three, right on the carpet. the carpet IS the hinge.
12. Make a pull tab. Using grille cloth folded over, make a loop and staple it to the bottom of the floor where the trunk latch is.
13. install. Turn the floor over. fold the wings "up" so they lay on the floor. Now it slips easily through your trunk opening. Lay the main section down. Fold the wings over and smooth the carpet so noone can see where the "seam" was. Vanishes like the seam in wall to wall carpet.

done.

You can get REAL fancy with this by inserting steps in between this layout to add fancy features. You are limited by your skill and imagination and tooling only.

 

Either use washers or a hole saw to make different sized circles.
Insert penciled in center.
Put flat piece of cardboard against the area u need pattern.
Then roll the circle w pencil along and you'll make the shape.
Cut cardboard pattern.
Repeat if there are areas you didn't get
Transfer to wood
Test fit.
If you want a completely flush fit, put down foil or aluminum tape in areas you have gaps
Fill in gaps w body filler/durglass.
Sand.
Cover with whatever material you normally use