Definitely nothing wrong with welding the snap brackets to the trailer frame. I have a regular Reese/Valley style weight distributing hitch and my brackets are welded to the trailer frame. Been that way for years with no problems.
That's not the snap up brackets, that is the cam plates.
2013 Jayco Eagle HT 23.5
2010 Ram 1500 HEMI with integrated brake controller, tow mirrors and Michelins LTX/AT2 275/65R20 max load: 3750 lbs. @ 80 psi