I don't think the title conveys what I'm trying to ask very well at all... But, I want to build a sub enclosure for behind the rear backrests of my truck. This is a somewhat narrow space, but from what I can tell of when the bench is folded down there should be just enough room for something viable. There are a couple of places that have examples of this location being used in their showcase/galleries as well - but I'd like to make my own box rather than pay someone else to. I'm noodling on ways to measure the space with the backrests up to make a box that makes best use of the space possible, and the only thing I have been able to come up with seems like a terrible idea that could go catastrophically wrong - and that is getting a massive bag behind there and filling it with expanding foam to occupy the space. Any ideas from the brain trust?
So you can get to it with seats down but not in there when seats are up, expanding foam in a bag is probably getting you somewhere as you suggest like when you make a race seat, How to form your own custom foam seat insert | Articles | Grassroots Motorsports
Snake a long ruler behind the seat while it's in the normal position. fix it in place with tape and cardboard against the back of the seat. Fold seat and measure the stick's position.
Reference photos. There's lots of empty space behind the carpet on the left, the steel you see where the seat bracket mounts is relatively straight all the way down. CAD had come to mind, but then seemed like it could turn into a frustrating process of trial and error. But also there's nothing lost other than my time so perhaps I start there. I think on balance I stick a pin in the expanding foam for now... doing it with the right material seems like it will cost more than getting someone else to do it, and doing it with cheap DIY spray foam seems like it stands a high chance of destroying my interior with a sticky mess if it somehow breaches the confines of the bag. I'm not sure I follow this - mind elaborating?
It's an expensive alternative to your binbag and expanding foam idea, but Instapak bags might be ideal - tape a few together, stuff em in the space put the seatback in place.
@sandys expanding foam was my first idea, but @David's Instapak's might have less of a risk of expanding foam explosions on a new interior. What about folding the seats down and having something mimic the edge of the seat from the hinge up to the anchor point on each side (think standing a 2x1 up each side of the truck). This would then give you a vertical to base measurements from. Hold a long straight edge against the two sides and you can measure from the back of the cab to the straight edge. Edit: Where are things like this available, but from the look of it it goes under your rear seats. I google'd "ram crew cab sub box" as I can't remember the make and model of your truck, or can be arsed to look for your post (for a new exhaust?) where you mention it.
Since it looks like you are going for super form-fitting, there's something to take into account: Some of the newer trucks have a pressure baffle behind the cab to help with closing doors and stuff.
