Which Tender? What float voltage does it keep? If you feel it (or have an IR heat gun) is it running hot?
Is the battery maintenance free or has caps so you can check fluid level? If you can, is fluid level low?
Can you measure /log charge rate as a daily average? How old is the battery and state of health to get an idea how lossy it *should* be? What battery?
Essentially I'm stating, look at everything. If all your ducks are in a row, it can work fine to do that. If one duck is out of line, it is no longer a line.
Oops, I forgot a few ducks. That truck? What is the normal parasitic draw, say after it has sat long enough to go into its deepest low power state (which may take an hour or more undisturbed including no hood or battery disconnect, etc)? You may not need the tender hooked up 24/7, if the charging strategy isn't the kindest or it is just more advantageous to put it on a timer box where it runs during cooler night hours and off in the daytime. Next the question is, is it good for a timer box to be at 115F every day.
If this is going to be a long term situation, and it's outside where it can get some sun, or even if not, if it is practical to mount a solar panel and string some cheap low voltage wire (even leftover CAT5 network cable, doorbell wire, etc, would work for this...) then I'd wonder about getting a solar panel array to maintain the battery, need not even be one with a proper battery charger circuit on it, just measure it during peak sun hours, and put a resistor in series to the battery so it gets around 80mA at peak sun. Check battery voltage after a week or two and adjust resistor value if needed. They are only a few cents a piece.
I don't really like *smart* chargers in high heat, as they tend to have electronics more prone to fail from heat, then are more difficult to repair if not something obvious like a blown capacitor. Blown transistor on the other hand, can let the battery go flat or if shorted closed circuit, cook the battery.
