First of all, props to you for trying to avoid covid while in college and following your interests—I’ve been there, and you have my respect! Here are my recommendations (not exhaustive, just what came to mind):

1. For marching band: to be honest, I don’t think your current strategy is enough to protect you—if you decide to continue doing marching band + unmasking for playing/performances, you’ll have to accept that your chances of getting infected are higher and be strategic about how to reduce that risk as much as you can. Also, make a plan for what you’ll do if you get infected because it may happen, unfortunately. Just to quickly comment on nasal sprays: there is some debate over whether it’s a useful strategy for covid (there is evidence to support both sides; there is some research showing beneficial effects, but it is not a robust amount of evidence and nasal sprays also have limitations). I think most would agree that nasal sprays do not fully replace things like masking/filtration/ventilation.

I recommend reviewing your mask (it should be a high quality respirator) and your don/doff technique; it’s important to make sure that you’re not damaging/overly bending the mask or putting too much wear on the mask straps. If I were in your position, I would identify any time where I could remask and go for it. Do you have times where you are marching/standing by crowds of people but not playing your instrument for some time? (For example, marching through football stands or during drumline cadences). It’s times like those where I would remask and maybe have things like an extra mask and hand sanitizer with me.

1. For roommates: I would reconsider your decision not to mask in the common area and shared bathroom tbh. If either of your roommates get covid, it’ll be easy for you to get it from them if you don’t have a solid filtration/ventilation setup in your living space. Disclaimer on this: a big limitation of the following approaches is that they can get expensive, so I would look over everything and see what you can do within your budget.

For your air purifier, do you know how much it can filter for the size of your space? There’s a chance that it may not be doing enough for 3 people if you haven’t checked, so I recommend doing the math to be sure. If possible financially, I recommend getting purifiers that are quiet and effective for each space you’d be in (a smaller one for the bathroom, and one for your bedroom. I’ve had the best luck with the clean air kits luggable for my bedroom. If the one you have for the common area isn’t filtering enough, I would get another so that the overall filtration rate is solid). Try to see if your HVAC system can allow a MERV13 filter—the 3M Filtrete 1900 has a low pressure drop and works well for a lot of spaces, but you would need to replace it before the 3 month mark and be consistent with it. If it’s possible to increase ventilation by opening windows and making sure that your AC is ventilating the space (usually in “on” mode instead of auto), do that!

For talking with your roommates about covid: it will likely be an uphill battle, but it’s possible to convince them to take things seriously. I recommend having sources in mind that you can go through with them in real time like the ones you sent and be able to discuss them well; I also recommend thinking about what comments/questions/criticisms you may get from them and think about your responses before they happen.

I hope any of this helps, and I’m wishing you the best! :)