I`m going to be doing my 2006 Outback and want an aggressive wash product (preferably foam) fo take off sealant. grime, etc. I would like to buy the GG Surface Prep, but only comes in gallon sizes and that would be sitting around for a loooooooooooooong time before before I could/would ever use that amount. I don`t have a foam cannon yet - only a foam gun, so not ideal but will work. Any suggestions?