One other important question:
Which fuse in the truck is blowing and what is its amperage rating?
I am guessing it is the 12vdc charge line to the trailer, but want to confirm it.
The Ford manual for your truck calls for Fuse #90 (Trailer Tow Battery Charge) to be a 25A cartridge fuse. Anything smaller in that slot would probably blow pretty quick. Just something to check to be sure they are replacing that fuse with the proper amp rating.
BTW, here's a like to the owners manual:
http://www.motorcraftservice.com/pub.../11f23og1e.pdf
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'11 Cougar 326MKS loaded with mods
'12 Ford F250 SuperCab 6.7 PowerStroke Diesel
Amateur Radio: KD2IAT (146.520)
GMRS: WQPG808 (462.675 TPL 141.3)