" have seen plastic
equivalents but asking around I've been told that the rats like to work

their teeth on them and they don't last long. "
My plastic bait boxes are now over 5 years old and nothing has gnawed
them. Rats gnaw for fun. When they are eating they aren't thinking of
gnawing.
The ones I use are designed to take the poison blocks. They need to be
sited carefully then left. Rats will not go near anything new. It may
take 2 weeks before the rat starts to use the bait box or trap or
whatever. I use poison blocks called 'tomcat' and find them effective
and safe. I breed poultry so need to control rats. I also have 18 cats
which hunt so need to be sure there is no secondary poisoning.
Luckily rats which have taken the bait, feel ill and ill rats like to
go and hide in their burrows so tend to die underground.
Seriously if you have a rat problem you MUST get it soprted out. If
you don't know what you are doing then call the council rat man. I have
heard terrible tales of children finding the poison, pets eating the
poison and one stupid person assumming his chickens wouldn't eat blue
grain (they did).