Has anyone used a compost loo in a Scottish winter? Worried about freezing temps slowing decomposition

I've been planning a small off-grid cabin build in Perthshire and the compost toilet question is one I keep going back and forth on. Most of the guides I've read are written with milder climates in mind — I'm looking at overnight lows that regularly hit -5°C or below from November through to March, and the cabin won't always be occupied, so the loo could be sitting dormant and cold for weeks at a time.

I've been looking at the Separett Villa 9215 and the Air Head, but I'm also considering just building a simple twin-chamber system under the cabin floor where it might benefit from slightly warmer ground temps. The Separett needs 12V for the fan, which is fine as I'm planning a 400W solar setup with a 200Ah LiFePO4 battery, but I'm not sure how the biology holds up when everything's basically frozen solid.

Has anyone actually run a compost loo through a proper Scottish or northern English winter? Does decomposition just pause and pick back up in spring, or does it cause real problems — smells, overflow risk, structural issues in the unit? Particularly curious whether anyone's added a small heat mat or reptile-style heating element to keep the chamber above a minimum temp.

@Gemma1981 mine's in a static caravan in a similar climate band — not Perthshire but gets properly cold. The decomposition does slow right down in winter, that's just reality. A few things that helped:

• Insulating underneath the unit made a noticeable difference
• A small 12v heating mat under the composting chamber keeps temps above the critical threshold (I run mine off a Victron system so the parasitic draw isn't a concern)
• Getting the carbon/nitrogen balance right going into autumn so the pile has good thermal mass before temps drop

The bigger issue for me was actually ventilation freezing the fan mechanism rather than decomposition stalling. Worth checking your chosen unit's fan is rated for sub-zero.

Separett and Air Head both have decent cold-climate followings if you're still deciding on a brand.

@Gemma1981 spent two winters in a motorhome parked up in highland Perthshire and this is a real concern worth planning around properly.

Key thing most guides miss: it's not just ambient temp, it's the thermal mass of the unit itself. A well-insulated cabinet around your composting chamber makes an enormous difference — even 50mm of PIR board can keep the active pile 8-10°C warmer than ambient.

A few practical points:

• Locate it on an internal wall where possible, or against a heat source
• Small seedling heat mat (12W) under the chamber works brilliantly as a low-draw solution
• Keep a Victron SmartShunt on your system so you can actually monitor that parasitic draw over winter
• Bulking material matters more in cold — drier carbon material helps maintain microbial activity

The Separett and Air Head designs handle cold better than most in my experience — the separation means the liquid side (the freeze risk) is dealt with separately.