Yes from memory they dont come in the Levo seat tube of size 34.9mm.
Therefore you will need a shim which are quite cheap.
I bought a 31.6mm Fox Transfer and bought the shim - no issues whatsoever.
Loads of info and questions like this already on the forum.
It really is down to how bothered you are about general wear and tear.
Invsiframe will reduce it, but not prevent it.
16W @ 240v is only 0.06A.
Its bugger all.
Campsite were 100% trying to do you over; they probably spotted you had an ebike which they knew needed charging.
The charger has to have some loss and isn’t comparable to a TV. Your charger is converting 240v AC to DC and also self managing the charge cycle via the BMS for yours and your batteries safety. This cant be done for free (tongue and cheek based on the fact you want zero loss).