I can't claim to have gone into things to the depth that Chris has, but I have a slimline chute I use for test flying.
I get it re-packed by RD Aviation at Kidlington (a fairly major chute supplier to the glider world) who charge about £30. They advised me that if it's used routinely as a seat-back to get it re-packed every 6 months, but for my occasional use, annually.
G