Kaos
I'm using a popup frame for my build. Had to have some spot welding done and straighten out the dip in the frame. As for weight you can find the original weight of yours by going to the online rental sites. They post so you can know which to rent for your car.
My tongue says it is 3500 so I only need to worry about my tow vehicle. The "C" channel it is built of is narrow on top so the sides will be attached to the the frame, if I can work around the extra plating they use to hang steps. (less than 1/8th thick).
The wheels are inside so you have to deal with the raised level. I am going to 5' and a drawer under the bed in back instead of front. You can also make or get longer hanger brackets in back and that will bring up the floor. (
someone please correct if wrong).
If you have the money have it sandblasted, taking off the paint is easy, scrubbing rust is a pain.
Check out the springs, 26 inches looks a little flat but they should be even. Some of the popups have heavier equipment and can make uneven loading while sitting.
Have fun and paint a color you really like cause you may not want to go through it again

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Miriam