I think a lot of people use Epsom salt as a preservative. I also travel quite often and had the same FSG dilemma... On my last trip I just took HETT instead, but maybe a batch of FSG with Epsom just for travel would be good (I think if I used it all the time it would dry me out...).
Mod CG since 5/10, 2b/3a, med width/density, low/med porosity, greying since 18, color over grey since 21

Hair hates: non-keratin protein, glycerin, sorbitol, agave, sulfates, polyquats, co-washing (flaky scalp), maybe aloe?
Hair loves: fewer/more natural ingredients, moisture

Scalp wash: Selsun Blue naturals or reg when desperate
Low poo: Giovanni TTTT
RO: SN - Strawberry, ES
LI: SNES
Style: HETT mousse, FSG if I make it, ??
DT: GVPCB
PT: GVPKP