We demonstrate the existence of dynamically stable multihump solitary waves in polaron-type models describing interaction of envelope and lattice excitations. In comparison with the earlier theory of multihump optical solitons [see Phys. Rev. Lett. 83, 296 (1999)], our analysis reveals a novel physical mechanism for the formation of stable multihump solitary waves in nonintegrable multi-component nonlinear models.Spatially localised solutions of multi-component nonlinear models, multi-component solitary waves, have received a great deal of attention in the last decade. In particular, recent studies in the nonlinear optics [1,2] and Bose-Einstein condensation [3] have shown that, under certain conditions and only in multi-component systems, the formation of dynamically stable localized states and soliton complexes is possible. Unlike their singlecomponent (or scalar) counterparts, multi-component (or vector) solitons possess complex internal structure forming a kind of "soliton molecules", which makes them attractive, both from the fundamental and applied point of view, as composite and reconfigurable carriers for a transport of spatially localized energy.Recent discovery of stable multi-component spatial solitons in optics [1,2] shed a light on the general physical mechanisms of the formation and stability of multicomponent localised states. Such states are often called multihump solitons due to multiple maxima displayed in their intensity profile. Usually, multihump solitary waves appear via bifurcations of scalar solitons when a primary soliton plays a role of an effective waveguide ("potential well") that traps higher-order guided modes excited in a complimentary field [2]. On the other hand, the multihump solitons can be formed as multi-soliton bound states, when two or more different vector solitons are "glued" together due to balanced interaction between the soliton constituents [4].Soliton bifurcations and binding enable the existence of multi-component localized states in many nonlinear models; these include bound states of dark solitons [4] and incoherent solitons [5] in optics, and multihump plasma waves [6]. Importantly, multihump solitary waves are also found in higher dimensions [6,7].The experimental and theoretical results on optical solitons [1,2] challenge the conventional view on multicomponent solitary waves in other fields of nonlinear physics. The main question we wish to address here is: Can stable multihump solitons exist in other important models of nonlinear physics? This is a crucial issue because, so far, the stable multihump solitons have been positively identified only in the nonlinear optical model of Refs. [1,2] that is known to possess additional symmetries, which might be the reason for their unique stability.In this Letter, we demonstrate the existence of dynamically stable multihump solitary states in a completely different (in both the physics and properties) but even more general model that describes the interaction of envelope and lattice excitations, a generalisation of the...