I welded the set-up on myself. If you do any welding which would be near the fiberglass shell, take it in small increments and let it cool down. Don't try to run a full bead all at once. Having done it the way I did, the trailer suffered no physical damage or blistering, although you will get some welding soot in the area. This just wipes right off though, so no problem.
The only place you will even find yourself in proximity to the fiberglass shell would be while installing the 1 1/2" forward crossbrace between the 3" main frame rails, which the front end of the 2" receiver tube gets secured to. Everywhere else, you are just metal to metal.
The old sewer hose bumper went away with this install. I now carry the sewer slinky rolled up in a 5 gallon plastic bucket in the Stow-Away box.
The "new" bumper is a 5 foot length of 3" X 3/16" thick heavy-walled square channel tubing, welded to the ends of the existing 3" main frame members. The forward brace is 1 1/2" X 1/8" square tubing, cut and welded to fit between the outer main 3" frame members (about 2 feet forward of the new bumper for strengthening the receiver tube mounting,) and is also welded onto the existing center longitudinal floor brace in the middle for reinforcement of the whole hitch assembly. The actual receiver tube (welded "fore and aft" under the whole shebang, is dimensionally 2" receiver tube channel, which is different than standard 2" square channel
. Most metal channel tubing is sold
as an "outside dimension", whereas receiver tube is sold
measured as an "inside dimension". Be sure to spec the right stuff you want to buy, or they'll probably sell you regular 2" square channel which will not accept a standard 2" receiver hitch.
As you mentioned, 17' Casita
tongue weights do tend to run heavy. I haven't had any problems with tongue weight
issues or handling issues whatsoever, and I carry (box wt. incl.) about 130~150 lbs. back there in mine. Even with the box installed, full of junk, and with me standing on the box lid in the driveway, (another 240 lbs. on top of the other 150 lbs.,) my neighbor, who is a pretty big and very strong man, couldn't even lift the tongue wheel off the ground.
Hope this helps. If you have any other questions about this install, hit me up.