Very good question and a very difficult topic, as there is no truly satisfactory answer. Trickle charging on a continuous basis definitely will cook the battery, in fact it will boil it dry! To work you would have to get the trickle charge current to exactly match the natural rate of decay of the battery plus any loads (eg the clock) that run with the ignition off - a very small current indeed and almost impossible to replicate. Plus the overall effect would be to damage the plates so that, although charged, the battery was no longer able to deliver the high current burst to operate the starter. Oh dear! It's as bad if you simply disconnect the battery and let it naturally discharge and then charge it up prior to wanting to use it.
The basic problem is that the action of a short very heavy discharge followed by a rapid recharge has been taken as the normal operating regime when designing the battery. Any other regime tends to clog up the pores in the plates and render them unable to perform when required.
The nearest I've seen anyone come to a successful charging regime is "pulse charging". In this the battery is allowed to run down naturally for a period - normally between 5 minutes and a 1/2 hour - while being monitored by a very sensitive voltmeter. When the battery reaches a preset level of discharge the voltmeter triggers a very heavy pulse of charging current for around 1/2 sec to restore the charge level.
I ran a fleet of small, car size engine, standby generator sets which were required to start up without fail in the event of a mains electricity failure. Such failures are pretty rare in this country - say 4 to 6 a year per set on average - so the duty was quite similar to what we want from our classic cars. With trickle charging the batteries were a complete nightmare - and we used really sophisticated trickle chargers with built in regulators that related the charge current to the charge state of the battery! With pulse charging we could get a couple of years 100% reliability from each battery.
Even so, pulse charging will not deliver the same sort of battery life as if you were using the car every day. I'm afraid it's a fact of life that the less often you use the battery the shorter its life! The opposite of natural assumption!
There are pulse chargers advertised in the classic car magazines or do a search on Google - I'm afraid I'm not familiar with what's available now.
The other moral of this tale is to buy cheap batteries frequently rather than trying to buck the underlying physics by buying good quality ones!
Chris