Had a 110 with 300 TDI when in Brazil. We took a trip from São Paulo to the Atacoma Desert in Chile. About 6,000km. Rover was well maintained. Took extra fuel cans. Nothing else and no issues. Kind of the reason for having a Diesel engine.
U-joint lube with grease is very important.
Regarding 300 TDI is important as you wrote, timing belt not at its end of life, this is 100.000km. And typical pain in the route is alternator (pulley, bearings) water or dust) so a spare alt can be a good amulet (it avoids to have such pain).
300 TDI, are now old vehicles, but if they are well mantained it is difficult to have trouble with them. I did a 15000km trip thru patagonia to Ushuahia and back and decided not to change oil nor filter (not to open bonnet in order not to bring mech trouble sources) and we ended without trouble and correct oil level.