Branding is relatively unimportant - cheap one at the big shed should suffice.

There should be no moisture present inside the internals of the timber paneling in cupboards along bottom corners of walls of cabin and any/all boot storage areas - also little black ants can be an indication of unacceptable moisture within walls.

thanks guys,
I'll keep an eye on those areas possum.

Moisture levels in what is considered dry timber should be below 12%. Timber will absorb moisture from the atmosphere naturally and will increase the percentage in humid or wet weather and lose moisture in dry conditions. Typical readings taken inside a dry dwelling including a caravan would usually be between 8 to 11% depending on the level of moisture in the air at the time. You can spend a lot of money on moisture meters, and if you are using them professionally then it is wise to buy a good one and spend the money, but for casually checking your own van, generally a cheap one will give a good enough indication if you have an issue or not. The firms I worked for had expensive models but since retirement I no longer have access to those so bought a little Aldi model which does the job more than adequately even though it may not be quite as accurate as the more expensive models. They only really read conductivity after all and convert that into moisture percentage and are good enough to indicate if there is excessive moisture present.

Many vans making use of composite panel construction still have wooden floors, cupboards, fixtures and other fittings and trim.

thanks again guys. some very useful comments.
travel safe and happy New Year to all.