Fitting extra siren outside

Hi guys, I'm new here but I have googled the forum to see if my question had already been asked/answered but didn't spot it. Sorry if I missed it.

I've just ordered my system and an extra siren and I've since seen that it is not completely weather resistant etc, etc.

My plan is to mount it on an external wall in a dummy alarm box to a) protect it and b) show that the property is alarmed. I'd also like to replace the batteries with a power lead to indoors so I don't have to go up and down ladders to change batteries.

Has anyone else done this with any success?

Thanks and stay safe!