I must be link-challenged. Another way to find the post is to click on my name (Isaac M) above the picture of my tow rig (on the left), select "Find Member's Posts", scroll down until you see the one titled "SOLD: 1989 19' Scamp
Fifth Wheel", click on the title
of that post and it will pull up the entire posting. If you read through the posting, I think that it will answer most of your questions.
I've never bolted one to the frame, but the local installer (who does the majority of trailer frame/axle repairs, services large trucks and busses, and does hitch installations for several local RV shops) said that it would be the best method for installing the brackets. The main reason was that it eliminates any local weakening of the frame that the welding can cause.
Feel free to contact me if you have further questions. If you PM me, I can provide my phone number if you have other questions.