It’s pretty easy though a bit more complicated if you have the plus model with the recirculating instant hot water feature. See page 14 of the manual here: http://www.truma.net/sites/default/f...ting-us-en.pdf
I would first refer you to any information in your owners manual on the chance the manufacturer has installed the unit differently than Truma proscribes. That said, close valves A, B, and E - shutting off the cold water supply, the hot water outlet, and the hot water circulation return. The unit is now effectively isolated from the RV water system. Open valve C - this is a bypass that feeds from the cold waterline near the Truma inlet to the hot water line near the Truma outlet. Go outside, open the unit, and rotate the big yellow chute out and downward. This drains the unit. Store the wire mesh filter in a safe place - it stays out for the winter.
Go winterize as normal. As the final step, open valve D. This is a drain line that will allow antifreeze to flow through the recirculating line back to near the Truma and then out to your catch can that you previously installed
. Close valve D when the flow turns pink.
Page 31 of the linked manual has plumbing schematics that show the various lines and which valve are A, B, etc.