For your 2006 Monaco Cayman 36, the best match a replacement potable water tank is the ICON Fresh Water Tank model WT3855. It matches the exact dimensions you provided: 50.75" x 22.75" x 5.75", with a capacity of 26.4 gallons. This tank is made of durable, impact-resistant polyethylene, BPA free, mold resistant, and certified to IAPMO and CSA standards, ensuring it is safe for drinking water. The product is priced at $451.81. While the turret connection size of 1.625" isn't explicitly detailed, ICON tanks typically support customizable fittings. If you need assistance verifying turret compatibility or additional fitting options, further support is available.