Used military surplus can really be a mixed bag of total awesome and total junk. We were lucky to have picked up two USMC Improved Bivy Covers a good while back.
We decided to wash them with Nikwax Tech-wash https://amzn.to/2Zxvx0k and used the Nikwax Wash-in waterproofing along with the Nikwax Spray on waterproofing https://amzn.to/2XC3eMk . Testing them in North Carolina thunderstorms in early spring gives us a good gauge as to how well the treatment worked.
- Gear Aid Tenacious Tape: https://amzn.to/2Dyz1q1
- Generic Gore-Tex seam tape: https://amzn.to/2IXaRZU
- Nikwax Tech-wash & Wash-in waterproofing: https://amzn.to/2Zxvx0k
- Nikwax Spray on waterproofing: https://amzn.to/2XC3eMk
- USMC Improved Bivy Cover (IBC): https://amzn.to/2EgoFwd
- Military Sleeping pad: https://amzn.to/2ZAejPF