Is using low wattage tube heater worth while?

 You share my consideration about winter lay up, the very cold temperatures and possible damage to water systems. Until last year I have been fortunate enough to garage store my van at home, but last year was a first under cover and outside temperatures down to -10c.I was worried, despite a full drain down of anything with water in it. 

The heaters you mention are usually very low wattage, I think typically 60 watts.

I know 500 watts in our caravan makes for a very comfortable autumn evening, but when it hits -6c outside as it did a couple of nights ago this would have made no difference. 60 watts would do noting, unless you could place one next to every tap, heater and joint in the system, which would obviously be impractical.

In the event that you did use a heater in the van then this would likely have a negative effect on damp levels as warmer air carries more moisture than cold air.

Colin

Bear in mind that your caravan has several essential vents so you could be wasting heat. You could also possibly encourage mould depending on temperature and conditions. 

I use one on a timer in the shed to prevent water pipes freezing up.

In the caravan NO!

Like thousands of others our van is in storage with no access to EHU. 

Battery off and brought home and trickle charged once a month.

Water systems drained down

Make sure the vents are clear and keep a few bowls of salt scattered around which we change every month or so. 

Jobs a good one.

Why do you put out bowls of salt? Yes, I know it absorbs moisture but, in view of the vents in your van, you are constantly soaking up moisture from the big outdoors and that’s why you need to change them every month. I recommend saving your money.

Having a full cover on your van and then having additional heating would to me encourage condensation which would more likely increase the risk of damp in my opinion. If you've drained down fully your van is just a tin box. I just removed all upholstery and opened all cupboard doors then on a nice day open all windows and rooflights for a blow through.

Regarding tube heaters, in my old Conquerer with dodgy blown air heating, while on site for long periods I had a tube under each sofa and one under the bed which made a big difference on cold mornings. 

Make sure that cover is well secured, I've seen a few vans in our storage damaged by loose fitting covers.

JK

I use trays of salt in the RV TW, no drop down vents at all as RV's have an electric LPG alarm instead so wet salt always means a problem

JK

Yours is a slightly different case, JK.

Most caravans/MHs also have wall vents where the fridges and microwaves are placed as well as gas vents. 

You're not wrong about fridges TW. I had to take the fridge out of my PVC and reinstall with the correct fittings as there was a serious draft at the top. When running on gas the CO alarm always went off. Could've been tragic. I'd only had the van 6 months but I did it myself as I really didn't trust the supplying dealer to sort it properly due to shoddy work previously.

Unfortunately that dealer had a fire at their East Sussex depot yesterday.

JK

Similar problems here, JK. Same dealer but different branch.

Warm air absorbs more moisture. Thing is if the equilibrium between humidity inside and outside the van will pretty much be aintaied despite what you do. What you can do though is limit water being absorbed and then stored in those materials inside the van itself. Good air circulation is key, not warmth.