My mates and I did a brilliant crawl down in Holmbush UK once (back in the days of very large fields and twenty-minute games). Four of us went in a line, right through the thick stuff, giving it hand signals, the works all the way.
We got to within rushing distance of the base, and then this tiny hissing noise we'd noticed became a huge rushing roar as the bottle came loose in Goatboy's gun. Sounded like we were letting off a fire extinguisher, amid much swearing and clouds of CO2. Needless to say, our attack on the base wasn't the crushing success we were hoping for.
Although with smaller fields and shorter games, the full-on cammo crawl is perhaps not so much of an option, you can sneak up to bunkers the opposition don't think are manned. Then pop out and give them the good news when they are firing at someone else! Just keep your butt low and and as much hard cover between yourself and the oppo's line-of-sight as possible.