After ordering the internal Progressive Industries and then spending a day realizing that the install would be painful, I went with the external surge guard and lockbox. My Eddie Bauer 27FB has no space behind the fuse box to install the internal one. Also I hated to have to remove the fuse box if I needed to get to the surge protector.
Funny thing, so I bought the external 30 amp surge guard and lock box and used it the last weekend camping. I realized on day 2 that if someone wanted to steal it, they would steal the whole cable and protector, as it wasn't locked to the shore power :-) Next time I will bring a lock cable.
I will say it was kind of neat to see the amps use. I didn't realize that the electric water heater pulled ~12 amps!