It depends on your main use: If your just doing mods and speed testing a Garmin eTrex will do you just fine. If you're looking to explore and go trail riding, then you should consider a new Garmin 76 series (discontinued, but can be found fairly inexpensively) or the updated model which is now the 78 series.
Regarding mounts, Seadoo does sell optional glove box lids specifically w/the 76 in mind. I'm pretty sure it will fit your '05. I have one on my '06 T and it works great. It does not fit the new 78. Other options would be found via RAM mounts.
