ckaiser

I'm looking at building this slider for my Toyota and have a couple of questions... I'm not a carpenter so please forgive my lack of knowledge...
First, how are the wooden side rails attached to the sliding piece of plywood?Is there a groove cut in the rails or do they just attach to the sides with screws/nails?
Second, how do the casters run on the guide rails?Are they inside?Outside?does it matter?LOL...
Third, do the casters themselves hit the rails or is it the wood mounting blocks?Or are the guide rails just there to keep it from getting too far sideways? If the latter, about how much clearance do you give it?
Last, have you had any issues with the slider warping over time?Here in the AZ desert, we always worry about wood drying out and warping. I'm guessing the side rails help keep the ply from flexing and maybe warping too?

Thanks much. It's a great design!

Charlie