If you have 30 amp plug and wire coming into the unit. And you plug that into a 30 amp supply. That's all that is going to flow into the unit and it won't (shouldn't anyhow) overload or heat up. No matter how many things you plug in and turn on in the truck. It's still only going to be able to get 30 amps from the supply.
I've also seen an adapter that has two male 20 (maybe 15 since both blades were parallel) amp plugs that wire directly together to a box that then has a 30 female socket to plug your 30 amp line to. If you can find 2 separate 20 (or 15) amp circuits to plug each of those males into your then going to have enough to run your 30 amp system.
Oh snap, I just did a google and here is the deal:
Dual 15 - 30 AMP RV Adapter For Honda, Yamaha, & Kipor Generator - Convert Two 15/20 AMP Outlets To One RV 30 AMP Outlet - Reviews & Prices @ Yahoo! Shopping
For you guys that "camp" and shows and stuff like that where they don't usually have a 30 amp rv hookup this would be a good thing to have. My brother goes to dog shows and he's used one similar to this. Key is to find two separate 20 amp plugins.