I'm not a professional by no means but a truck cap would be my choice but there would be some pros and cons of both.
Pros for cap: covers everything nicely, no trailer to drag around
Cons for cap: Being able to get to everything in the bed of the truck easily, bed of truck will stink if running a generator
Pros for trailer: plenty of room, bed won't stink of gas from generator
Cons for Trailer: hauling it around, manuevering it(if you're not good with trailers, everything is out in the weather..
(Add your pros and cons)
Also, I used to own a 95 S-10 a few years back and I know S-10's have a "sagging" problem stock. As if it isn't bad without anything in the bed of the truck, adding a lot of weight (water tank FULL, generator..) to the truck will make it drag or even the weight of a trailer will make the truck sag a great amount so you might want to look into helper springs or air shocks to help level out the truck if you haven't already. Just my 2 cents from experience.
