The SPX Voltec one is by far the most reasonable priced one, ($495) and, since I have two of them, I have seen it's internal construction, and it is very well designed, with a rubber seal that should protect it against anything short of an actual flood. It has provision for the electric connection to be made from the bottom, as well as one from the back, and both are completely sealed until you break or drill one out.
I also like the design of it, with it's coiled cord hangs over the top, instead of a straight cord that would end up laying on the floor/ground.
Jerry, #536 2011 Crystal Red Volt,
2012 Diamond White Volt, saved from the crusher,
1975 Cosworth Vega,
1988 Formula Fiero,, also saved from the crusher,