I tend to agree with Bumpyroad here - If you're buying a vehicle regardless for towing, buy one that is flat towable from the factory. If you know you're going to flat tow, don't buy one that requires expensive modifications to do it.
The pickup with a cap on it sounds perfect for carrying a bunch of bikes. A pickup can be very useful for lots of other things, too.
If you're comparing the cost of adding a cap to a pickup to the cost of a Remco lube pump addition to a van, don't forget to factor in the cost to install that lube pump. That will add another $1k or so to the cost of the pump (unless you're handy enough to do it yourself).
I think you'll find, you can get a cap for a pickup for less than what the lube pump would cost.
As to specific experience with a lube pump: We installed a lube pump on our Kia minivan and towed it the first year/season we owned a MH. Great product and great company that stands behind it pretty well. Worked OK for a while, but then had some leaking problems that pretty much destroyed our trust in the pump, didn't want to use it anymore. Something about watching the pump bust a leak and spew 6 quarts of tranny fluid like a huge geyser all over everything, that image is kinda burned in my head and I never could trust the pump after that, haha.
Dealer fixed it (at Remco's expense and theirs), and it has worked fine ever since that incident. However, I had/have issues trusting it since then, so we ended up trading our other vehicle in for one thats flat towable from the factory, a Ford Fusion Hybrid. Towing is a bit more stress free for us now, when we don't have to worry about that pump.
Sooo, thats why I say, if you are buying a vehicle anyway and can avoid dealing with a modification like a lube pump, you should. :)