Is this a union show? What contract are you on? And how many shows a week?
Of course, let your producers know well in advance. Also, if possible, make sure that person gets to watch the show from the house at least once, and if possible as well, that they meet the cast ahead of time.
Normally, the sub observes once, then is observed once before taking it over for those few days, but that may depend on how complex the show is technically, and how well the sub picks up.
For your, there are a few options: In an ideal world, you are on an AEA contract that has formal sub SM language which (if I remember correctly) requires that person being hired for a minimum of a week and may include a health allotment. For your employers, it would mean one additional check in that week.
Other people choose the option you mention, to simply be paid directly as a sub ? which would be full amount for however many days, but before taxes are taken out. That person will be working at least 4 and possibly more days, depending on show specifics, cast size etc.
You might start by reaching out to SMs you know and trust in your area. Some will only work under contract, and some will prefer covering without the formality. But either way, it will give you a head start before broaching the topic to your producers.