RAM Part RAM-B-174-AQ6U : What a great idea.  RAM has combined their best in the business motorcycle clutch mount with a weather proof case for your GPS!

The mount is made of marine grade powder coated aluminum.  

The case, made from high strength composite, is a medium/wide size waterproof box with a clear Flex-Lens allowing you to press and operate the buttons of your device when secured in the Aqua Box. The box offers the ability to lock the device inside with a small keyed padlock (not included).  Your GPS sits inside safe from the elements!

This Aqua Box measures:  4.0 inches high, 6.0 wide, 1.75 inches deep.

These fit the majority of GPS models with 4.3 and 3.5 inch diagonal displays including:
Garmin: Nuvi 200 200W 205 205W 250 250W 255 255W 260 260W 270 465T 350 360 370 650 660 670 680 750 755T 760 765T 770 775T 780 785T 850 855 860 880 885T 1100 1200 1250 1260T 1300 1350 1350T 1350LMT 1370T 1390T 1390LMT 2555LT 2555LMT 2595LMT
Garmin: dezl 560LMT, 560LT
Magellan Maestro 3100 3140 3200 3210 3220 3225 3250 4350 4370
Magellan RoadMate: 2210, 2210T, 2220-LM, 2230T-LM, 5220-LM, 5230T-LM, 5235T-LM
MIO C220 C230 C310 C310x C320 C520 C710 C720T H610 MOOV 200 210 300 310 320 330 340 350 360 370 380 M400 & Knight Rider
Navigon: 1200 1210 1300 1310 1400 1410 2000S 2090S 2100 2100 MAX 2120 2120 MAX 2400 2410 2510 3300 3310 4310 4350 5100 6300 6310 6350 7310 8410 8450 7100 7200T 8100T
Magellan: RoadMate 1210 1220 1340 1430 1440
TomTom: Ease Start ONE ONE-S XL XL-S 125 125SE 130 130S 140 140S 325 325S 330 330S 335S 340 340S 350 IQ GO 930 920 920T 740 730 720 630 530 520
TomTom Start Europe: 20, 25, 60
TomTom Start: 45, 45M, 45TM, 50, 55, 55M, 55TMT
omTom VIA:  1535, 1505, 1435, 1405