I'm all in favor of isolation transformers, but think you should find and fix the electrical problems on your boat first, rather than using the isolation transformer to sweep them under the rug.
Also note that if you are suddenly going through zincs faster than expected, you have DC leakage of some sort. AC leakage won't impact zincs, only DC.
It seems you have two problems to unravel.
Tanglewood is right on all counts, especially identifying any issues rather than covering them up with a xfmr. One area of confusion, however, is the fact that the shore power cord, while it conveys AC power, will facilitate galvanic corrosion, which is DC in nature, when plugged into shore power and if not equipped with a transformer (xfmr) or functioning galvanic isolator (GI), and even if the shore power is off. GI's can block galvanic voltage up to about 1.4 VDC, while the ability of an xfmr to block is is unlimited because there is no actual connection between shore and boat ground. The current crop of GI's are far better than those of 10 or 20 years ago, in order to be ABYC compliant they must be fail safe, meaning if they fail, they retain the connection to the shore safety ground, while no longer providing corrosion protection.
Your problem may be the GI itself, legacy galvanic isolators, some more than others, were not of the highest quality, and not ABYC compliant, so it may not be doing its job. These are easy to test,
https://marinehowto.com/testing-a-galvanic-isolator/ With no functioning GI, 4 months for anodes may not be unusual if you are in a marina, as your anodes could be protecting your neighbors' vessels.
An isolation xfmr is the gold standard when it comes to isolating shore power and potential galvanic corrosion sources (as well as making for a safer AC system overall where Electric Shock Drowning is concerned
https://stevedmarineconsulting.com/electric-shock-drowning-and-elcis-explained/ ). However, I would only ever consider installing one that also boosts. Without the boost function, you can actually find yourself in a worse scenario than with no xfmr at all, in the event you plug into 208 service, which is not uncommon. With no xfmr if you plug into 208, you end up with 208/120 VAC aboard. With a xfmr, you end up with 208/104 aboard. If, on the other hand, your system is 120 VAC only, this is not an issue and no boosting is needed.
Charles no longer supports their boosting xfmrs, and their control boards do occasionally fail, however, an outfit in Fort Lauderdale does offer support and an improved board.
Transformers, especially the boosting 240 VAC variety are bulky and very heavy, making placement a problem on some vessels.
Hubbell offers an isolation xfmr that does everything the Charles unit did and then some, including a versatile digital display.
If you have 30 amp 120 VAC inlets that you use simultaneously, you need two transformers.
If you do need a 240 VAC xfmr, you can get an optional version that will accept a 120 VAC input, enabling you to plug into a 120 VAC dock outlet and still have limited kW 240 VAC aboard.
One final note, the same shore power transformer can be wired for polarization or isolation, the hardware is identical, the installation is different.
There are many nuances associated with shore power transformers, most of which are covered here
https://stevedmarineconsulting.com/wp-content/uploads/2019/12/ShorePowerTransformers181-04.pdf
