Wow ! how big's your gas bottle then....
If it's anything like the boat safety scheme, then you have to have the minimum sensible amount of flexible to allow for connection of the bottles.
You may wish to increase the size of the gas pipe, if it is a long run, normally I think they used to use 3/8 " or 10mm you may need 15mm. :nenau
It depends on your gas appliances, on boat safety all appliance are switched on and they test the gas pressure at the furthest point from the bottles.
You are allowed a small pressure drop.
You need to ensure that the copper pipe is secured adequately there is a maximum distance allowed between fixing clips, but not sure what it is. :nenau
For sealant, I have used Calortite, it looks the same as red hematite, and I use it as if it was hematite on sump plugs, oil fillers etc, and the plugs are always easy to get out and no oil leaks. Also I have used it on non potable water fittings etc.
Clean up with meths.
Hope this helps.
I think :nenau the regulations on the boat safety used to be, if you pay someone to do the gas work, THEN.. the installer must be GAS SAFE.
Regulations on the caravan installations could be different.