You could try the CMHC classifieds section. Also I guess dear old EBay is an obvious choice, or a caravan breakers. There’s always the risk that you may get something that doesn’t work properly unless you can see it installed and working before you remove it.
I've asked Haymarket admin for a caravan accessory classified section and a private message service for this forum several times but to no avail.
Now that Future plc have taken over and Lizzie Pope stayed with Haymarket I don't even know who to ask :dry:
The CMHC members adverts is hosted by another company who have a large sales website. So the CMHC benefit by having more active visits by memembers and non members and the hosting company also benefit by their increased number of “ hits”. Also the hosting company offer an enhanced sales advert at a number of prices as extras in case the seller wants increased visibility. So it’s a symbiotic relationship.
Future could consider it as if it attracted more hits to PC then they could potentially grow revenue too from their magazine sales and advert hits.
For Facebook users the Practical Caravan page doesn't appear to have any restrictions on advertising.
It doesn't appear to attract much traffic however, but there are various buy, sell and swap groups on Facebook which might be worth a try. Enter 'Caravan Buy Sell Swap' into the FB search box and there will be several results.