trailers
The box truck would be nice, definitely plenty of room for hauling stuff but they don't fit through a regular garage door too well.
I guess the big question to ask is how much are you looking to spend? I'm considering a trailer myself as well vs. getting a second van. Good and bad for each.
I agree with Shane T. A 6X10 single axle trailer is what I'm leaning towards right now. A 6X12 will give you a little extra room but you lose out on hauling capacity. Both trailers have the same gross hauling weight capacity even though they are different sizes. Because the 6x12 weighs more, you lose hauling capacity because the trailer itself weighs more. Did I explain that correctly? If you go online and look and the break down between the two sizes you'll see what I mean.
You'll have to give up some room to maintain the ability to haul heavier equipment.. ie; the loss of carrying a fresh water tank that Shane alluded to. Or switch to fixing up a 55 gal drum of being able to carry some fresh water for those times your customers don't have or you can't easily access a water line. I've got a 100 gal fresh water tank and am deciding on whether or not I want to have it cut in half and re-welded so I can still have fresh water on board, save on space and weight for any extra equipment I might want to put in my trailer as I grow my business.
I know you will need to carry insurance for it.. the trailer sales guy I talked with confirmed that but I don't recall the exact name for the type of policy/coverage. It's a policy to cover and damage or liability if the trailer were to come off while driving etc.. he said it wasn't too expensive but a good idea to have none the less.
Your next option might be to upgrade to a 7x14 size.. you'll get more room, extra towing capacity because I think those all have dual axles and in some cases electric brakes, which is nice to have for obvious reasons when you have that much weight bearing down on your ass unlike a 6x10 or 6x12.
My recommendation would be sticking with a quality name brand; Haul-mark, Interstate are some good ones. Steel frame rather than aluminum. Some guys may try to talk you into saving weight by going with aluminum frames but if you are going to using the trailer a lot and carrying heavy loads, aluminum won't stand up as well as steel will and then you'll be buying a new trailer in another few years because your frame cracked.
Go with 3/4 in plywood floors, 1/2 is too thin. Make sure if you by a used trailer, have the axles and hubs checked out. Some guys may not have lubed the hubs or cracked an axle and that's why they are selling.. hubs alone can be $350 each or more to replace plus labor.. get E-Z lube hubs many makers have switched over to making all new trailers with E-Z lubes but some don't.
Good luck on your purchase. Living in Jersey, your located in a great area for picking up a trailer at a good price even for a new one. A trailer with the features I've mentioned will cost roughly $1800-$2100 depending on the maker, features/extras and warranty. Same trailers in Maine will be $2800-3000. If gas wasn't soooo much now I would drive down and buy there but I'd spend more on gas now so that negates and cost savings.