I need (this weekend ideally) to build a simple bed box for the back of my van. I thought I’d wedge all my questions in one post. So bear with me please!

It’s to sit on the opposite side to the sliding door over a wheel arch. Originally the van had a shelf arrangement when we bought it that sat behind the rear seats and when they were folded flat formed a double bed. However this meant to get the bikes in I have to remove the wheels and wedge them underneath the bed shelf. So instead I intend to build a box on one half with a lid that is the existing shelf bit cut not quite equally in half length ways which will fold out and form the bed platform with some kind of gatefold legs yet to be designed…

I am a geologist not a carpenter, rocks yes, Wood; no.

The existing bed shelf which is shaped to fit the van is 18mm ply. I was intending reuse this cut in half lengthwise and to build the box frame out of 44mm square planed with 18mm Ply walls thinking the ply will help support the load?

I would like the lid to hinge up to use the box for storage, however I’m I sure how the hinge the lid as it also needs the second leaf to fold out to form the bed and I’m not sure what kind of hinges to use so I can screw them in to the face of the plywood as obviously I don’t want to go into the grain (layers). Similarly I need to make some fold down legs, which will need when extended to be flush to the underside not quite sure how to hinge those either to make them sit flat for transport as well.

I’m planning on using some heavy duty latches as I want to be able to remove it if necessary. Can I just bolt these to the van ply lining?

Finally I was looking for a really cheap Mitre / drop saw, as the simplest way of ensuring square cuts. Any recommendations? Thinking the £40 Screwfix / Toolstation end of the market?

Thanks in advance!