Douglass did mine and I opted for the frame mounts incorporating my fast-guns. Today I might choose a different tie-down system, depending on how critical the alignment would need to be. I just picked up our new Mammoth last weekend in Portland and I can't utilize any of the 4 factory grab points on the camper. Knowing this I had some custom ones built and powder coated white. The 2 fronts bolt to the swing-out brackets and the 2 rears are about 12" further back. I used the factory 3-bolt pattern and drilled out another 3 bolt pattern just beyond the power slide gearing. Because my Douglass body has a narrower taper in the back, they work fine, however the fast-guns do block the cabinet doors. No real problem though-
I can send some pictures to your email if you want. Drop me a PM if interested-