Sorry if this sounds rude, I am just annoyed by people using Toxapex as more of a Tank, and without Regnerator. :P
You typically should just Poison whatever Toxapex needs Poisoned with Toxic, and Burn is for literally every physical attacker that threatens Toxapex. So long as you play intelligently and sometimes predict, Burning something that you'd rather Poison shouldn't be a problem. Baneful Bunker is bad because Toxapex doesn't need a protection move to Poison, Baneful Bunker only poisons contact attackers, and to add salt to the wound, it doesn't Badly Poison. Venoshock+Merciless is useless due to both of Toxapex's attack stats being below 60. :P
TL;DR your better off using an actual special attacker instead of making a Wall do a Tank's job. :P