i mounted my amps on the back of my box and made some brackets to attach it to the rear wall. since the true bottom of the box is 8" or so off of the floor, i mounted my capacitor to the bottom of the box. ill have to post a few pics to show ya.
if your really short on room, you could just throw a bazooka tube or two behind the seat. theres not enough room to mount a sub under bucket seats. i have a friend that runs 2 8" jl's and it sounds amazing in the truck and yo dont get everything rattling ouside

 

Exactly correct. Do not underestimate the strength of wood glue. After glued the glue is much, MUCH stronger than the wood itself. The nails, screws are merely clamps until the glue dries.

That said, I would, and have done countless times, built a backless box that will house the 10's. Sound dampener on the back wall and it will work great.

 

Google mtx thunderform

 

I've probably built 50 speaker boxes in my day and I always used drywall screws to hold the MDF together and sealed the inside edge with silicone. I can't believe anyone would actually nail a speaker box together but I see several people do it that way. To each their own I suppose...

Putting 10's behind the seat of a standard cab is going to be a tall order unless you look up to Danny Devito. I had a single 8" JL 8W6 behind the seat of my 94 when I had it and I built the box as small as I could and only had to give up one click on the passenger side of the seat. I'm 6'4" so a big box just wasn't an option as my knees were already only 4 inches from the dash. Those 10's probably need about 1.5 cubes each to sound right, and if you go that big it just isn't going to fit behind the seat very well. If it were me with a standard cab truck, I'd either build the box without a back and glue it to the back of the truck or I'd get a sawzall and cut the back of the truck out and seal it with some accordion boot. I did that to an Isuzu truck I drove before I went Toyota and it sounded great. I just built the box in 2 pieces and slid them together from the inside to the bed and screwed it together. Biggest drawback to this is that the accordion boot was $7 a foot 19 years ago. I hate to see what it is now...