I might be the wrong person to reply to this thread, since I **like** bugs: I used to make my living doing live animal shows, so I've kept many species of scorpion, centipede, millipede, tarantula, cockroaches and spiders (including Black Widows and Brown Recluse).
The bugs can't live in your van unless they have food and water. So by denying them those things, you make it less inviting for uninvited guests. "Water" you can't really do anything about, since most critters can live happily on the condensation inside the van. "Food", for some species, can also be difficult to remove completely, since cockroaches for example can eat the insulation from your wiring, your rubber floormats, or each other. But keeping your floors assiduously clean of crumbs can at least help keep them away. The bugs you really want to watch out for are the various kinds of "carpet beetles"--these can get into your food supply (they like grains and flour) and wreak havoc, and they are damn hard to get rid of.
As far as safety, keep in mind that there are in the US only one species of scorpion that is potentially hazardous (the Arizona Bark Scorpion), and only two types of spider (Black Widows and Brown Recluses--tarantulas, despite their fearsome image, are not harmful to humans, and in fact they make great pets), and none of those species particularly like being around people. So it is tremendously unlikely that you will be killed in your sleep.
Lenny,
I GENERALLY do not eat or store grains or flour (being Ketogenic) so I might not have that trouble. I use ground almond flour as my flour. I try to store in glass that is airtight too and don't plan to change that. I will keep that in mind though about the occasional rice. My sister had a tarantula as a pet too. As for only one scorpion being deadly, I could die from MANY bug stings like bees, other scorpions, wasps, etc. etc. not just one, being allergic and extremely sensitive to venom. Since you know so much about these bugs like roaches, is there any way to roach-proof your wires or floor mats, or even your rig? P.S. I saw centipedes too in Hawaii, always dead! You must have had an interesting profession (in a weird way!)