Sealant - how much of it do you really replace?

This week I've just replaced the awning rail sealant on my 'banger' 1993 Bailey - if an older caravan can be said to 'bang'. It's far, far easier buying new mastic on a roll rather than in tubes. After using tubes in the past I decided that the job made undersealing a car seem a clean job! No mess at all this time though, and a far more consistent thickness of mastic when it's simply rolled on.

At this stage though, I've only replaced the mastic under the awning rails. I know that, in an ideal world, you should really replace all mastic throughout the 'van, eg around windows, door, roof lights, strips along the body, lights, etc. However I'm taking the view that these other areas are less susceptible to damp ingress and not replacing mastic there. I accept that damp can get into the other places, in fact my previous 'van suffered damp around a door aperture and a rear light wiring hole. However I don't have several spare days to replace all the mastic, which is the time it would take given how long it takes to remove old mastic.

On the previous 'van I tried to replace mastic around just one window, but found that the frame never fitted as well again, which in itself would increase the risk of damp.

What do other members do in the real world?