While I am a raw beginner to model boats, I have been building RC model cars for many years now. Here are some of my current collection (all Tamiya):
My DT02 Sand Viper:

Mods:
Rubber sealed bearings throughout
Etronix 27t rebuildable motor
RW Racing hardened steel pinion
Ansmann alloy shocks with Tamiya seals
Tamiya alloy hexes
Carson all-terrian wheel & tyre set
My DT02 Desert Gator:

Mods:
Rubber sealed bearings in front wheels, rear hubs and diff, metal-shielded bearings in the gearbox for reduced friction
Etronix 27t rebuildable motor, rebuilt with cut and trued comm, stiffer springs, zapped magnets and optimised timing
RW Racing hardened steel pinion
Tamiya alloy oil shocks
Tamiya aluminium ball links
Tamiya ball diff
Tamiya alloy hexes
Tamiya aluminium wheel nuts
My re-re Hornet:

Mods:
Rubber sealed bearings throughout
Tamiya Sport Tuned motor
My Rising Fighter:

Mods:
Rubber sealed bearings throughout
Etronix 27t rebuildable motor
RW Racing hardened steel pinion
Ansmann alloy shocks with Tamiya seals
Edit aluminium wheel nuts
My CC01 Pajero:

Mods:
Rubber sealed bearings throughout
Etronix 60t rebuildable motor
RW Racing hardened steel pinion
Ansmann alloy shocks with Tamiya seals
GPM aluminium ballraced steering
GPM aluminium front suspension arms
GPM aluminium servo mounts
GPM aluminium damper mounts
GPM aluminium front hubs
GPM steel front universals
JunFac rear 4-link kit & underbody bash plate
JunFac front skid plate
JunFac hardened steel propshaft
JunFac alloy & steel sliders/running boards
JunFac alloy spare wheel mount
Fastrax Kong 90mm tyres
Tamiya alloy hexes
Tamiya diff lockers
Futaba servo winch
Proline roof rack
It is this model that made me want to build a RC model boat. Having built the Pajero for scale/trail competition use, I wanted to maximise my scale points by building it a trailer. That got me thinking that a functional trailer with a functional RC vehicle on it would be a good idea, so now I am looking to build a Robbe Katja or similar 1/10 scale motor boat, both for use on the water, and for use as a scale accessory for the Pajero.