Would you have extra information ? On the first link given by @Jezza, the product title is " Reacher Tech completely waterproof D65L150 Inrunner 5000w". I looked carefully for the “Splash Waterproof” and did not find it. Sure, the sealing needs to be done carefully.
They manufacture ESC’s and seem to sell the matching speed controller which might be a good surprise.
When you compare both series side by side, you are not sure that so little volume (65x150) and so little power (5KW) can pack so much torque ? The torque of the 65x150 inrunner is twice higher than of the 83x95 outrunner… 
… with same motor volume.
| RT Motor | D83-325 | D83-270 | D65L150-100 | D65L150-80 | |
|---|---|---|---|---|---|
| Construction | 24N/20P | 24N/20P | 18N/6P | 18N/6P | |
| Turns | 5T | 6T | 4T | 5T | |
| Working Voltage | 22.2-50.4V | 29.6-58.8V | 40-60V | 40-60V | |
| Max RPM | 16380 | 15876 | 6000 | 4800 | |
| KV | 325 | 270 | 100 | 80 | |
| No Load Current @8,4V | 4.3A | 3.8 | 1.5A | 1.2 | |
| Max Output Power | 10KW | 9.6KW | 6KW | 4.8KW | |
| Peak Current (A) | 335A | 320 | 150 | 120 | |
| Max Efficiency | >88% | >89% | >92% | >92% | |
| Net Weight (kg) | 1.91KG | 1.90KG | 2.5 | 2.5 | |
| Dimension (mm) | D82.8*L95 | D82.8*L95 | D65*L150 | D65*L150 | |
| Shaft Diameter (mm) | 12mm | 12mm | D10*30mm | D10*30mm | |
| Max Torque (Nm) | 10.5 | 11.5 | 11.5 | 12 | |
| Wire Length | 6AWGx300mm | 6AWGx300mm | 8AWGx180mm | 8AWGx180mm | |
| Connector | 10mm plug | 10mm plug | 6.0mm plug | 6.0mm plug | |
| Working Life | 10000H | 10000H | 10000H | 10000H |