Mildew is a real problem and prevention is the only real way to deal with it. A tent must be packed away bone dry with any potential sources of damp removed. This could even be from insects that have been packed away with the tent! Or from the core of guylines that were not dried unravelled to ensure deep moisture was removed by air flow.
Once mildew has set in you have to stop it spreading. Kill off the spores with a very mild solution of one part Milton or white vinegar to ten parts water − rinsing off well. Marks are harder to remove and we have not yet found a satisfactory solution although we have read a few ideas on Facebook from Outwell fans. Whatever some can be quite aggressive so be very careful...
Besides the cleaners from the likes of Storm you can get canvas cleaners from the caravan market and mildew cleaners for sails from the yachting market but we have not tried any of these. The Camping and Caravanning Club used to have a data sheet on tent maintenance - worth looking on their website.
Remember to reproof the tent after cleaning.
We recommend that you annually maintain your tent. Therefore we have created a guide for how you can mend the tent best:
Airing and Reproofing:
First of all erect your tent make sure it is dry, then put waterproofing on it. We have heard good things about fabsil, but we also carry our own products for this, it is of course your decision. There exists both spray products and brush products. Spraying is easier and gets you a nice even coating, our water guard will take about 2 bottles for one tent.
Let it dry then go through all the seams with seam sealer. And let it dry again, then give it a good shake after some hours and pack it down again. This is called Airing, and will keep your tent in mint condition for years to come.
We advise that you first use a dilution 1:10 of miltons to make sure to kill any bacteria, then hot water with soap and a soft sponge, and then reproof afterwards. This also goes for the carpet.