Since we are going to sell the M, I didn't want to drop 4-5k on a trailer. I took a good look at the trailer itself. It looks good, other than the tongue that aspires to be as solid as swiss cheese!
I found a professional welder to come over and weld a new piece of 3x3 1/4" thick steel to the trailer, replaced the outer tongue member and new receiver. Spent $300 on the welding service (6 hours) and $50 for the steel, $35 for the hitch member, and 175 on a new surge brake unit.
We need to realize that even the aluminum Mac trailers have a STEEL tongue. This could still happen on an aluminum mac trailer!
The problem is there is no where for the water to exit the tongue once it gets in. The hole in the end for the brake line is in the middle..so water always sits and rusts away... day after day.. year after year..
The only thing holding the tongue together, literally, was the paint!
So if you have an original trailer.. take a good hard look at the tongue!
Here is a 'Before' picture- Looks 'acceptable' - no holes... its only as thick as the paint.. No kidding..

here is the tongue after it is cut out.. the paint is gone..so is all the steel!! YES the bottom picture IS the same tongue as the picture above!!

New outer member and tongue - note how much thicker the new 1/4" steel is (factory was 1/8) Note that I did coat the inside with some rustproofing paint and a chassis paint over THAT
