Short bed is really a exercise in fixing weight distribution. You are going to have to make a long frame sticking out the front and put a lot (heavy)storage containers on the tongue to make it work.
You need to figure about 10% of the total weight should be on the tongue to give it good road manners. That means empty you have to have enough weight in front of that bed to balance the tail. If you fail to do that they the trailer with get squirrely on you and is dangerous.
I looked at this long and hard once myself and a Long bed made more sense because it would take less to get it balanced correctly. Bob the back down to short bed length was what I though of doing. That would keep the weight bias in front of the axle where it needed to be.
I also thought about taking a short bed and cutting the ends off and swapping them so you could run the bed backwards to help move the weight bias forward. In the end it seemed like more work then it was worth and went with a conventional trailer.
The problem is a truck bed is a LOT of extra weight that you don't need is what I finally figured out. It needs a frame to support it and depending on the bed you use it may be double wall. A conventional trailer with a well designed rail is a monocoque chassis. The frame is the body so you can make it pretty light with a little planning.
I have a 4x6 enclosed trailer (it was a fixer upper) that I picked up for $200 off craigslist that doesn't weight 300lb empty and I can sleep in it. You would be VERY hard pressed to get a truck bed trailer balanced correctly (empty) under 600lb.
They do look good when done right. If you got the bed cheap or free thats a plus. If looks isn't a major concern you might want to look for a 4x6 or 4x8 conventional.
Remember...weight is the enemy. The lighter it is the less power it takes to move it.
my plan: preferably a long bed but, well see what i can come up with, probably scratch build the frame and put a mild body lift on there so i can tuck a water tank under there (some where in the 50-100 gal range) to accommodate drinking, dish washing and showers (im looking into a small water heater cause y not travel in style,
So you plan to pull 400-800 pounds of water? Just how long do you plan to be away from a water source that you need to pull half a Honda CRX with you?

Just what were you planning to pull this with and to where? Might want to modify that plan a little.
20 gallons conservatively used is enough for 2 people for 3-4 days. My Airstream that is set up for boon docking only carries a max of 40 gallons (and you could sneak an extra 6 in the water heater) and that is considered a 3-5 day supply for 2 depending on how conservative you are and that is with a toilet using it as well.
Zodi makes a nice small water heater you can pick up for around $100 at Walmart.
http://www.zodi.com/web-content/Consumer/zodihottaptravelshower.html
Showers are: quickly wet turn off water, Soap up and wash wet hair then quickly rinse. Should be able to do it with about 2-3 gallons for a woman with long hair and 2 gallons for a man with short hair if you are being conservative. If you have somebody that cant control the amount of water they need to take a shower with (my 5ft 90lb wife is one of these and can wipe out our 40gallon water heater no problem) you want to get this.
http://www.zodi.com/web-content/Consumer/zodiextremeshower.html and make sure they understand thats all they get so they don't wipe out your water supply. That will fix the let the water run while the suds problem REAL quick.
