Great ruling. That should probably be the default ruleset to be honest. For normal play (where players have the luxury of prepping and building their characters - which we don't here) I might restrict it a little to where you have to have a copy of the ritual handy - pay the nuyen cost but no karma cost - in order to cast it. Not sure what the nuyen cost for a ritual is, but I'd probably make them either free or at the most 500¥ (like Detection and Health spells). Considering that each ritual has a fairly steep reagent cost, it might just be better to assume their free, which brings us right back to your ruling here. Hmm. So yeah, great ruling.
However, in our case, I don't know what rituals might be useful. We could do a Ward ritual, but it takes hours to perform and lasts weeks - probably not the sort of evidence we want to leave behind and not the sort of time we want to be stationary and exposed before it takes effect. In fact, most of the useful rituals take hours to complete, so they aren't likely worthwhile for us here. We could try building a temporary lodge, which would act as a Circle of Protection, but that still takes hours and then only lasts until sunrise (or sunset, but since it's already dark...). So, unless I'm missing something, this might not be useful. I half suspect that the description for Circle of Protection might be wrong - it says it takes Force hours to perform but only lasts Force hours, while most things that last Force hours only take Force minutes to perform (and since it is so small and breaks when someone leaves, it is unlikely they meant for it to last Force weeks or days). In that case, that could then be a useful ritual.
But, barring that, I'm fine leaving it in the van. We could place a watch there if we really wanted to, but that might be a bit much - while we don't want this falling into the wrong hands, we probably wouldn't mind much if it were to "walk off". And besides, without comms, leaving a single person there to guard it might be pointless.
I'm certainly open to ideas.
