I've never heard about the vinegar - that may work! However - I put my "A" up in the back yard - got the deck sprayer (pump sprayer), mixed 1 cup bleach with 1.5 gallons of water and sprayed it both inside and out. Then I let it sit for about 3 hours and then rinsed it thoroughly. I wouldn't have done that - but when I put it up - it just SMELLED! BAD! (like mold/mildew). However - the bleach killed the bad stuff and dulled down the stains. Tent actually looks quite a bit better now.
The key to WATERPROOFING your tent is to apply some kind of sealer to the fabric when it's standing.
As one person said - a deck water repellent is an excellent idea - HOWEVER - do NOT USE A FLAMMABLE one! Believe it or not - this will leave your tent flammable to a large degree. A burning death is not fun at all!
I use a water-based sealent put out by a company called VALSPAR - it's in their "SEVERE WEATHER" collection of products. It's NOT an oil based product and is white in color.
You'll need 2-3 gallons with a deck sprayer on your "A" tent.
1. First Coat: Spray inside and out and let dry
2. Second Coat: Spray inside and out and let dry
3. Third coat: Spray outside only and let dry
then you take it down. You'll notice that the fabric has about doubled in weight and seems 'thicker' - but it's waterproof!
In any case - if you have questions - ask - "BEEN THERE DONE THAT!"
Your Obedient Servant,
John E. Schultz
1st Sgt. ANV Signal Corps Detachment - CSA