A Potential Cargo Trailer Convert?

Hello,
I've been eyeballing teardrops and other small trailer options for years. For some reason, I had always considered a cargo trailer to be too heavy. Then I realized they're only margainlly heavier than most 5x8 tears. A Carry-On 5x8 weighs 890-lbs. I could even get a 5x10 and gain a side door and two more feet of floor space at 930-lbs. I cannot go too heavy because of my tow rig:
With a cargo trailer purchase being fairly easy and convenient, I may actually make a move this year!
My goal is to have something in which I can haul my wheels and tools for autocross events, have a dry, shady retreat to relax at the events (electricity and air conditioning would be awesome), a way to move things too large to fit in the car (no more than 500-lbs), and, lastly, an enclosed unit which could be used for camping. I've only camped once since I was a kid. Who knows? Perhaps the camping will really take off with my daughter and we'll do it more frequently than I expect.
Enough blabbing! I came to ask a question or two:
1) I've learned a lot about insulating the interior by reading here. It's a tad scary to notice these things are mostly body frames bolted to a chassis with aluminum rivetted to the outside and 1/8 wood screwed to the inside.
But what about the FLOOR? Sure, it's plenty strong. But do many of you insulate it? Also, would it be wise to weatherproof the underside somehow? It's just bare wood!
2) Would getting a 5x10 over a 5x8 be a bad idea? I plan on installing electric brakes on whatever I get. Other than stopping power, is there something I may be overlooking about the extra two feet and 40-lbs?
3) How are most of you addressing air conditioning? Are you using roof mounted units? Or are you cutting a hole in the wall an using a less expensive unit? I've seen a few slick set ups. But I'm sure I haven't seen them all.
In case it matters, I'm looking to get a swing-open rear door instead of a ramp. The 5x10 is attractive because of the side door. I'd likely convert that door to something more conventional with a window or porthole and a door knob. If I stick with a 5x8, then I'll likely cut a hole in the rear door and install a smaller "RV door" for convenience. I appreciate anything thoughts you might have.
Thanks!
Scott
I've been eyeballing teardrops and other small trailer options for years. For some reason, I had always considered a cargo trailer to be too heavy. Then I realized they're only margainlly heavier than most 5x8 tears. A Carry-On 5x8 weighs 890-lbs. I could even get a 5x10 and gain a side door and two more feet of floor space at 930-lbs. I cannot go too heavy because of my tow rig:

With a cargo trailer purchase being fairly easy and convenient, I may actually make a move this year!

Enough blabbing! I came to ask a question or two:
1) I've learned a lot about insulating the interior by reading here. It's a tad scary to notice these things are mostly body frames bolted to a chassis with aluminum rivetted to the outside and 1/8 wood screwed to the inside.

2) Would getting a 5x10 over a 5x8 be a bad idea? I plan on installing electric brakes on whatever I get. Other than stopping power, is there something I may be overlooking about the extra two feet and 40-lbs?
3) How are most of you addressing air conditioning? Are you using roof mounted units? Or are you cutting a hole in the wall an using a less expensive unit? I've seen a few slick set ups. But I'm sure I haven't seen them all.
In case it matters, I'm looking to get a swing-open rear door instead of a ramp. The 5x10 is attractive because of the side door. I'd likely convert that door to something more conventional with a window or porthole and a door knob. If I stick with a 5x8, then I'll likely cut a hole in the rear door and install a smaller "RV door" for convenience. I appreciate anything thoughts you might have.
Thanks!
Scott