I need more gas in my truck... GM put one piss-ant sized tank in these. Anybody done a aux tank with gas? I'm thinking 40-60 gallons in the bed. Probably a fuel tank/toolbox combo. Use a stock or generic style sending unit/pump combo and wire it to a gauge and timer in the cab. I can make the fitting to tie a fuel line to the fill neck hose so I can pump it to the stock tank. My biggest concern is the venting or tying the vent to the evap system in the truck. Anybody tried it?