Hi Leon,
The trees 'might' be causing a little bit of signal scatter since they are in your Line of Sight to the tower but, shouldn't be causing too much trouble really.
I assume your caravan is of the 'metal skinned' variety? The walls of your caravan may actually be presenting more of an issue?
The other thing that might be causing interference is, powerlines & whether or not you have anything in the caravan that is transmitting/receiving.. this might include a microwave, tv reception, etc... other electrical signals in close proximity can cause interference with the signal...
This link will show you the frequencies used by carriers for 3G/4G etc...
May or may not be helpful in determining if there is a source of electrical/RF interference messing with your signal.
https://www.whistleout.com.au/Mobile...rk-frequencies
My advice, try your laptop outside & see if anything improves... or not...
If you get improvement in your signal when you remove either the caravan or the trees from the equation then, as long as you 'fault find' one issue at a time, you should be able to figure out which is causing you the most problems.
For the caravan, you might be able to get a signal booster, similar to what are installed in cars with fixed, hands free kits... sometimes an aerial is put on the roof to improve signal strength...
Something like this perhaps:
https://www.telstra.com.au/coverage-...ension-devices
For the trees, see Multiweb's response...
Good luck with it, hopefully you can find the source of your problems...