I went back to re-read the NTSB report and the link no longer worked for me... so with that said....
I'm not certain what the NTSB was looking for when they tested for toluene, because toluene is also a major component of 100LL avgas. It's the major component that is used to bring the octane of the fuel up so that less lead may be used to obtain the LL-claim. Carrying any flammable fluid in the cockpit is a hazard....not just TCP.
Having said that, I carry my TCP in it's plastic bottle which itself is kept inside a tough, airtight cip-type plastic bag, and so that it cannot "tip" over. (Even if it did tip, it'd still not likely leak due to the bag.)
I also squeese a bit of air out of the bottle so that it's slightly collapsed before going airborne, so that there is space for expansion. The bag also is devoid of as much air as possible.
I still intend to develop a firewall-mounted storage box similar to a battery box for such items, and also oily rags and spare oil, etc. (In all my spare time I should have it ready for the next owner.)