I wanted to post an update! Mr Meli is all healed! Thank you to all that responded. I'm going to document exactly which route we ended up going on with pictures, incase anyone else ever goes through a similar situation.
So as I said in the original post, there aren't any bunny savvy vets anywhere near me. Meli had a lump that we initially thought was caused by a botfly. I took him to a rabbit rescue, out of someone's home, for help and they too were unsure what caused the lump. The guy lanced the mass and it seemed to be hollow. He did remove a chunk of meat but we were unsure if it was a dead warble. The texture was shriveled and looked like a piece of flesh vs Traditional botfly larvae. Anyway fast forward a few months, his lump wasn't healing and remained open, as the pictures above show, and he was losing a lot of weight with minimal appetite. I tried to take him to several vets, but none of which knew anything rabbit related and I was put on a waitinglist to see an exotic vet roughly 2 hours from me. That's when I turned to the forum and made the initial posting.
Since the future appt with the exotic vet was close to a month out and because Meli seemed to be getting worse by the day, I decided to continue self treatment. And I did crazy amounts of research, learning everything about their anatomy, treatments, sicknesses, how to dose meditation, etc. I figured anything was better than just waiting and, if I couldn't take him to a vet, I was going to become as knowledgeable as possible to help him myself. His weight went under 5 lbs, and he is usually a solid 8, his poops became shriveled (I went from changing his litter box every 3 days to once every 6 cuz it was barely wet or soiled), and he wasn't eating appropriately. His mass also started producing foamy puss, which I noticed while cleaning, and which hadn't been happening before, so I was concerned about him becoming septic. I purchased Bactracillin G 300,000 iu, and started dosing him, along with giving him electrolytes for his gut health.
(If anyone isn't familiar with how to dose rabbits for penicillin, here is a breakdown. It is 300,000 ius per 10 lbs. So 1 full ml of penicillin if your rabbit is 10 lbs. Because Meli weighed 4.5 lbs his dose of penicillin was .45 ml. Penicillin needs to be stored in the refrigerator, and you can use a 22 gauge syringe to dispense. The injection is subcutaneous, so under the skin, and because he was so sickly I was also giving him critical care and smashed banana with a feeding syringe. That helps maintain the rabbits gut flora.)
Along with the antibiotics, I decided to band the mass. It wasn't connected to anything along the muscle wall, and was hanging low enough to drag on the floor when he'd walk. It was constantly bleeding too because it hung so low and was obviously irritating him. I was skeptical but because he was literally withering away I was willing to try it. I used a castration band for goats, my brother held him, so I could have both hands free, and after his daily wound cleaning I placed the band behind the mass. He didn't flinch, or squirm. He didn't look in distress, and I had a cuticle cutter to cut the band handy, just incase it looked like he was hurting at all over the next few hours. I made him a little vest cover the mass and to prevent him from biting at his chest. He hates any type of clothing or collars, so he kept trying to slip his vest, but it did its purpose.
After day one, I examined the mass and went to clean it. If felt cooler so I knew the circulation was slowly cutting, and I noticed it wasn't as plump. Day 2, Meli had his full appetite back. He literally ate his body weight in food and was constantly hungry. By day 3 I noticed his poops were more hydrated and not as shriveled. He was drinking lots of water again and was having zoomies around the house. By day 4, the mass has become hard like a dried prune and I couldn't even stick a syringe inside to flush it. (We were flushing the mass over the last few months with a solution of iodine, water, and near the end some apple cider vinegar. Like a super diluted solution that was a light golden color). By day 12 Meli bit off the entire stabbed mass including the band. The wound was pretty closed but we kept triple antibiotic ointment without lidocaine (because lidocaine can literally stop their heart) until it was completely healed. Meli is now up 3.5 lbs and is eating normal, has his loads of energy, runs and has zooming, has hefty poops (his litter is being changed regularly again), and is back to being curious and sassy. I did take him to the vet when the appt came around just to make sure all was ok, and he said had I not done what I did, he would've died.
I'm just thankful it all worked out ok, and my bunny is back to being fully healthy! I hope this helps anyone who may experience something similar. I'm attaching pictures of him lounging today, along with what the mass looked like after day 4, and a photo of him in his vest (because he's too cute). And if you look at him lounging today vs when he was wearing his vest you can see his change in weight. His face is full again
