I've checked under my 1990 1.9DG to check the condition of the front to back cooling pipes as we're going on a longish trip next month. They look like original plastic ones. I thought they were rubber but I think that was just a layer of road crud on the underside

Is it a good idea to replace them or only if they're showing signs of active leaks? I've not noticed any but the van's about to go in for a service and coolant flush so it would be the time to do it.
If I take the plunge and change them I'm planning on using the Brickwerks stainless kit. Is it possible to fit them without taking the tank off given it come in 2 halves per pipe?
The pipes to the heater matrix don't look so great either so I'm thinking about replacing them at the same time with the Brickwerks EPDM hose.
Are there other things that it makes sense to do at the same time as a job like this? It had a new tank and fuel lines about 10 years ago.
I took some pictures from the underneath



Thanks in advance!
Patrick