Hey I just recently did this to my M416. I purchased two 2" I.D. receiver tubes from Northern Tool and welded them into my frame. I have one on each side just in front of the fender and one in the rear.
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I then welded a couple of scrap pieces of 2" O.D. square tube I had to fit in any one of three locations
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Then mounted a 3/4" X 24" X 68" piece of wood I got from Lowes.
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There are no table legs to trip over in the middle of the night. HOWEVER - the perfect height for sitting is also crotch height so round of them corners!!!
When I get my lid built I will mount the wood to the inside bottom of the lid.