I think you will find most Whites land based coils labelled as "waterproof" are only intended for use under a couple of feet of water, and are not rated nor pressure tested for 30-40m depths, and that in itself will be a limiting factor with the SPP. If you were just shallow water hunting then you probably could devise a reasonably waterproof setup, although still with no 100% guarantees the unit won't leak (a bit of a risk on a $1500 detector). Most owners of detectors converted into a sealed housing, either use them in shallow water, or to be made as a "splash proof" unit. I have also seen a few FBS detectors converted as such, though none were ever built with 30-40m water pressures in mind, nor tested in such environments.
Here's a Whites TDi SL mounted in a waterproof casing, though only splashproof, and not waterproof to any great depths.
http://z7.invisionfree.com/whitesgoldmaster/index.php?showtopic=701
There was also mention that the Tdi SL circuit board will fit directly into the Beach Hunter housing, so the SPP will more than likely fit as well, though once again only for use at shallow depths.
http://www.findmall.com/read.php?73,1556887
Most Pelican cases are only rated as splash proof as a minimum, whilst at their highest waterproof rating is limited to only 10m on specific cases, so you can probably discount the idea of utilising them pretty quickly for the deep stuff.
Either way, you don't have to spend ATX/Infinium type money on a waterproof detector either, a bottom rung Tesoro Sand Shark PI is waterproof to 200 feet, and only comes in at around $1000, and a Garrett Sea Hunter MK2 is only $300 dearer, also rated at 200 feet, and is considered a very good underwater detector. You could then save the SPP mainly for goldfields duties. Personally I think this would be a more financial sense over the custom build, but once again, just my opinion.
